Field of the Invention
The present invention relates to a method of producing a toner, the method used for a recording method utilizing an electrophotographic method, an electrostatic recording method and a toner jet recording method.
Description of the Related Art
In recent years, the high definition of a toner image has been required in an electrophotographic field. In order to form a high definition image, it is important that toner particles have uniform performance among themselves. Therefore, it is effective to equalize the particle diameters of the toner particles, to provide sharp particle size distribution and to suppress the occurrence of a variant particle having a low circularity.
A “dissolution suspension method” has been known as a producing method which can easily achieve the sharp particle size distribution and high circularity of the toner particle. The dissolution suspension method includes dispersing a resin solution in which a resin is previously dissolved in an organic solvent in a dispersion medium, to form a droplet of the resin solution, and thereafter removing the organic solvent to obtain a toner particle.
In the dissolution suspension method, a water-based medium is commonly used as a dispersion medium. However, when the water-based medium is used, enormous energy and time are required for a washing step and a drying step after the particle is formed. So, in recent years, a method of producing a toner wherein carbon dioxide is used as a dispersion medium has been proposed.
In this method, after a dispersion in which a droplet of a resin solution is dispersed in carbon dioxide as a dispersion medium is formed, carbon dioxide is further introduced into the dispersion, and an organic solvent in the droplet is extracted and removed to obtain a toner particle. The method can reduce pressure after removing the solvent to easily separate the obtained toner particle from carbon dioxide as a dispersion medium, and produce the toner particle with energy saved and at low cost without requiring a washing step and a drying step.
When a toner is produced according to a dissolution suspension method using carbon dioxide for a dispersion medium, it is necessary to use a dispersant functioning from a droplet forming step to a solvent removing step in order to achieve sharp particle size distribution and a high circularity. The dispersant covers the surface of the droplets of the resin solution, to suppress the aggregation and sedimentation of the droplets, which provides stable dispersion of the droplets and maintains the dispersion state of the droplets. Therefore, the selection of the dispersant is important.
Japanese Patent Application Laid-Open No. 2009-052005 proposes a method of producing a resin particle, wherein carbon dioxide in a liquid state or a supercritical state is utilized as a dispersion medium, and a resin fine particle containing behenyl acrylate and methacrylic modified silicone is used for a dispersant.
Japanese Patent Application Laid-Open No. 2013-137535 proposes a toner produced in a dispersion medium containing carbon dioxide using a resin fine particle. The resin fine particle contains a resin having a comb type structure including a segment having an organopolysiloxane structure and a segment having an aliphatic polyester structure.
In this method, a droplet is formed in the amount of carbon dioxide introduced less than that of the method of Japanese Patent Application Laid-Open No. 2009-052005, and carbon dioxide is further introduced to remove a solvent. Therefore, the viscosity of the droplet when the droplet is formed is maintained in a comparatively low state, which can provide a toner particle having good particle size distribution to a certain degree.